Double stack
P4's new stack is a slip-formed concrete structure that's 430 tall and 67 feet, 7 inches in diameter. Designed by Pullman Power, it took one month of weekdays to erect at the average slip-forming rate of 1 foot per hour. Inside the stack are two fiberglass-reinforced plastic flue gas liners. Each liner is 26 feet, 7 inches in diameter (Figure 7). Both flues were field-fabricated and assembled on site. The resin used on the structural FRP wall was Hetron FR992. A 15-foot-high vertical mandrel was used to spin twelve 30-foot "cans" per flue, which were then placed in the chimney base and jacked into place one at a time.
7. Two in one. The interior of the new, 430-ft tall stack, showing the two fiberglass-reinforced plastic flues, one for each generating unit. Courtesy: Washington Group International
Construction challenges
Pleasant Prairie has the largest megawatt capacity in We Energies' system and in the state of Wisconsin, making it critical to complete the project on time and within scheduled outage windows. Key aspects of the outage work—ductwork tie-ins; integration of a new, plantwide distributed control system upgrade; and electrification of the distribution system—were completed without impact to the outage schedule. Because most systems were tested prior to tie-in, start-up of the new equipment had minimal impact on plant availability. This major project also was brought on-line concurrent with other plant projects to complete a turbine overhaul and install a new superheater.
SCR construction had to take place above the existing coal delivery system and draft fan equipment, requiring significant crane support. The FGD was constructed in proximity to the plant's ash-loading operations. Plant generation and delivery systems were not impacted during project construction. The project achieved more than 1,000,000 work hours without a lost-time incident.
Sharing the risks and rewards
The engineering, procurement, construction, and commissioning proposal prepared by Washington Group in the fall of 2003 established an initial price for the project, which then became the starting point for negotiating the target price. We Energies and Washington Group shared cost, schedule, startup, and performance risks as an incentive to reduce costs while meeting the target price. The target price estimate and associated technical description formed the baseline from which the project's execution was monitored. As the design was fleshed out, changes in the estimate basis, and savings and cost additions, were tracked, recorded, and agreed to prior to being finalized. This approach ensured that the project team remained focused on the project's goals while controlling its costs.
The project was initiated by a limited Notice to Proceed delivered to Washington Group's Engineering department in November 2003. The first eight months were spent developing a well-defined project scope to establish the target price, starting with a "bottom-up" cost estimate. This kind of estimate required a significant expenditure of engineering resources to define the scope of work and to perform the technical studies and evaluations needed to establish the plant design basis and arrangement. It also necessitated finalizing configurations of the electrical and instrumentation systems, the material-handling approach, selection of fans, etc.
Once that was done, summary specifications were prepared for all equipment, subcontracts, and bulk materials. The specifications then were used to solicit vendors and establish target prices. The initial critical activities included the award of the contracts for FGD equipment supply and for designing and erecting the stack. Upon completion of the civil/structural design in the spring of 2004, a full Notice to Proceed was issued and construction began.
—Steven Gebhart (steven.gebhart@wgint.com) is the project manager, Dennis Pennline (dennis.pennline@wgint.com) is project engineering manager, and Ira Brodsky (ira.brodsky@wgint.com) is lead process engineer for Washington Group International on the We Energies Pleasant Prairie Power Plant Air Quality Control Upgrade Project. Dan Bichler (dan.bichler@we-energies.com) is project manager for We Energies.
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